In the past, images (pictures) were taken with cameras utilizing film. In recent years, pictures have also been made by using solid state detectors which are electrically sensitive to various wave bands of energy received through an optical system. The electrical charge from each detector becomes an electronic signal which is eventually changed into the picture element (pixel) of an image. Existing solid state imaging systems which record more than one wave band, depend on the registration of the analogous picture elements of the different wave bands to record and integrate the response from the different wave bands. Such an apparatus is known as a multispectral remote sensor.
Such solid state systems have found wide use in airplane, satellite and space vehicle imaging because the data can be recorded in digital form and transmitted via wireless in near real time.
It is necessary to define several terms:
Detector refers to the smallest solid state element in the apparatus for sensing a particular wave length of electromagnetic energy arriving from the scene. The detector response in turn is processed into an electronic signal which is known as the picture element (pixel) of the resulting image.
Registration is the ability of the solid state image apparatus to merge different sets of electromagnetic energy that is sensed by the detector elements, to form a clear picture.
Resolution is a measure of the information (fineness of detail) that can be displayed in the resulting image.
Systematic offset, as used herein, means that each detector element of a given array of detectors records a signal from the scene which is offset from a signal recorded by an analagous detector in the two cartesian (cardinal) directions by a fractional amount the denominator of which is equal to the number of wave bands utilized. For example, if three wave bands are utilized (one for each array of detectors) the offset will be one third of a detector element which results in a number of subpicture elements equal to the square of the number of wave bands, in this case nine.
As stated, there were many attempts to improve resolution of such solid state imaging apparatus. But there has not been much of an attempt to improve resolution by the multiple use of the same size picture element in a given apparatus. The two exceptions that are noted is, for instance, the solid state camera that was recently developed by RCA which utilizes two green bands in which the detectors are offset to each other. As is known, the resolution in color television transmission has been improved by making one color band of higher resolution then the other two. As a result, this band improves the resolution of the picture. This principal is utilized in the RCA camera as well as the offsetting of the two green electromagnetic bands so as to form some subpicture elements or subpixels. However, this principal in the RCA camera is utilized with only one wave band and as such is of limited utility as compared to the instant invention.
Another solid state imaging apparatus that partially utilizes the concept of overlapping pixels is the multispectral sensor system (MSS) of NASA. This system utilized overlap of the picture elements of the same wave band in one direction. The images are focused by an optical system using a mechanical scanner. However, the overlap is done only in the direction perpendicular to the direction of movement of the satellite and the overlap involves the same wave bands. Accordingly, the resolution of the images could be improved further by utilizing the principal of the instant invention. Further, picture elements have been made smaller and smaller so that there could be more of these picture elements in a given image so as to improve the image resolution but this is a relatively costly way to improve resolution. Nevertheless, it has been found that with the same size of picture elements, the resolution of the picture can be improved markedly by using the principals of the instant invention.
Accordingly, it is the object of the present invention to improve the resolution of multispectral images formed by picture elements of a given size and system cost.
The object of the invention is accomplished by means of apparatus and method set forth in the Figures, and in the information set forth herein below.